Size encapsulation is a measure of the degree that a starch film covers the surface of the yarn making up a warp preparatory to weaving.
The sizing machine or slasher utilizes a hot liquid starch bath into which several thousand individual strands or ends of yarn which make up the warp are immersed. After immersion, excess liquid is squeezed out by passing the warp between tightly compressed squeeze rolls. The warp is then passed over several sets of steam heated drying cylinders which evaporate most of the water. An even dispersion of solid starch is left on the yarn in the form of a coating. The starch penetrates the soft yarn, and this helps to keep it from breaking off. Size encapsulation is expressed in degrees from 0 to 360 as an average measure of coverage around the yarn.
Very fine hairs protrude out of the surface of spun yarn before it is sized. One of the main objects of sizing is to bind these hairs to the yarn and cover both with the smooth size film to protect the bundle from the abrasive forces of the loom where the warp will be woven into cloth.
After the warp is dried, adjacent ends or strands may be stuck together by excess size. The adjacent ends are separated by pulling them alternately over and under round bars which extend through the entire warp. During this process, some of the size actually covering the hairs breaks off and the hairs once again protrude outward.
The degree of size encapsulation around each yarn in the warp has always played an important role in reducing loom stops due to warp end breaks. This importance has increased in recent years as a consequence of increasing loom speeds made possible by the use of air instead of a projectile or shuttle to propel the filling yarn through the shed or opening between alternate ends or strands of yarn in the warp.
When lots of hairs protrude off the yarn making up the warp, they impede the air blast and, if sufficiently severe, cause the filling stop motion on the loom to be activated.
This effect was discovered in the mills three years ago, which prompted us to furnish moisture sensors between drying sections on the slasher to assure the optimum amount of moisture in the yarn at the moment it contacts a hot drying cylinder of the final dryer. Our moisture controls are being used now to regulate the steam pressure on the first dryers to achieve this objective.
In connection with this effort to maximize the degree of size encapsulation, we have developed a means of monitoring it on the slasher while the warp is being sized. Not only can the effect of moisture in the warp between drying sections upon size encapsulation be observed and maximized during processing, but other variables can also be adjusted to maximize size encapsulation. These include the moisture in the yarn, the temperature of the liquid size, the temperatures of the drying cylinders, squeeze roll pressure, and tension in the yarn as adjacent ends are separated.
The means consists of two photoelectric optical sensors which convert the passage of hairs on the yarn to a proportional voltage.
One of the sensors is used on one sample yarn at the entry into the sizing process and one is used on a sample yarn at the delivery end of the process.
Since the hairs protrude outward when parts of the size film are lost, the number of hairs remaining compared with the number of hairs on the unsized yarn is a measure of the lack of degree of size encapsulation.
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Since the warp is stretched by varying percentages depending upon fiber makeup, each unit of yarn length at entry is stretched out to a correspondingly longer length at delivery. No compensation for stretch is necessary, because the output voltage from the sensors is proportional to the number of hairs passing through the sensors per unit of time. By this means, the number of hairs on a unit length of yarn at entry is compared with the number of hairs on the same unit length stretched at delivery.